When using automatic production equipment which operates at a very high speed to produce articles at a very high rate, especially in the case of production of cigarettes, there are special requirements and burdens on quality checking. Each individual article which has been produced must be reliably checked and, if a flaw is detected, the flawed article must be separated out. In practice, pneumatic testing processes are used for this purpose and some of these are described in German OS No. 2,324,055; OS No. 2,653,735; and AS No. 2,422,276.
When using pneumatic inspection procedures, the end of the cigarette must be pneumatically sealed to a tube for delivering testing air for forming a testing signal, and the seal presents a special problem. For such testing processes, it is necessary to seal the end of a cigarette during a very small time interval without damaging the end. At the same time, the sealing arrangement which connects and delivers the testing air must be placed against the cigarette in such a way that the feed line of the testing air lies precisely coaxially in relation to the cigarette.
Known testing arrangements use so-called testing tubes which involve essentially cylindrical or slightly conical sealing bodies with an axial bore and with a connecting or sealing surface at the end toward the cigarette which is generally in the shape of an axially opening hemispherical cup. The radius of the open end of this surface is larger than that of the cigarette to be tested so that a seal is formed primarily because of the fact that the cigarette end is slightly compressed in a tapered shape while the edges of the cup extend axially beyond the terminal surface of the cigarette and without, however, contacting the outside wall of the cigarette. Other arrangements are equipped with hemispherical cup-like members which are, nevertheless, placed onto the cigarette ends in the same manner as the tubes.
Practical experience with such sealing arrangements as, for example, illustrated in German OS No. 2,324,055, have shown from evidence at the contact surfaces that the contact between the sealing body and the cigarette deviates from concentric coaxial contact because of otherwise imperceptible imprecisions. It also appears that the eccentricity in any one tube remains the same but it differs from one tube to another. Apparently purely by accident, some tubes also show concentric or nearly concentric contact. These experiences confirm what has also been found by additional testing of the cigarettes, namely, that because of sealing faults and because of eccentric feeding of the testing air, the test results include many mistakes resulting in the rejection of cigarettes without flaws despite the high expenditure for these mechanical devices.